iWork etc - unused space at the side

I'm new to Mac - very new - and one thing that frustrates me so far is that most apps I open do not fill the screen left to right to make use of it. Surely there must be a way to make Pages fill the screen but I haven't found it yet. Can anyone help? I thought the green button would do it like on Windows programs but apparently not.

A common complaint from switchers, it's a non-issue really. To re-phrase the above, the green button will stretch the window to be as big as it needs to be, thus not wasting any window area within the window. In other words, it's smarter than a "full screen" default. I like to be able to see, and access, my icons along the sides of my screen, as well as another open window underneath, which saves me a "trip" to the Dock.